Bonding structure of circuit substrate and instant circuit inspection method thereof

ABSTRACT

The present invention provides a bonding structure of circuit substrates and an instant circuit inspection method thereof. The contact pad design of the bonding structure has an instant inspection ability of circuit connection in bonding two circuit substrates. In two bonded circuit substrates, the signal inputted at the circuit part passes the conductive particles to the first contact pad, and then passes the conductive particles again to the detecting part from the first contact pad. Therefore, measuring the output signal can inspect the reliability of the circuit connection of the bonded circuit substrates. If the output signal is the same as the input signal, the bonding structure between the first contact pad and the circuit part is validated, or, if not, the bonding structure is invalidated.

1. FIELD OF THE INVENTION

This invention relates to a bonding structure of two circuit substrates,and, more especially, to a bonding structure with instant inspection forreliability of circuit connection in bonding two circuit substrates.

2. BACKGROUND OF THE RELATED ART

FIG. 1 is a top schematic diagram showing the bonding structure betweentwo circuit substrates according to a prior art. When two circuitsubstrates 10, 50 are bonded, two circuits on the two circuit substrates10, 50 are electrically connected to each other via contact pads 11 and21 at the bonded interface between these two circuit substrates 10 and50. Especially, in assembling the display panel, such as the liquidcrystal display (LCD), the organic electro-luminescence display (OELD)and the plasma display panel (PDP), the surface mount technique (SMT),tape automated bonding (TAB), chip on glass (COG) and chip on film(COF), the aforementioned technique are generally employed.

FIG. 2 illustrates the conduction principle of the circuits on circuitsubstrates 10 and 50. The circuit on the circuit substrate 10 is coveredby an insulating layer 41 and the end of the circuit is exposed to formthe contact pad 11. The contact pad 21 on the circuit substrate 50 iselectrically connected to the circuit of the circuit substrate 10 via ananisotropic conductive film (ACF) 30. The anisotropic conductive film 30includes an insulator 31 and a plurality of conductive particles 32distributed in the insulator 31, and the conductive particles 32 aredisposed of an insulating film on their surfaces. The anisotropicconductive film 30 is disposed between two contact pads 11, 21 andthermally compressed as the circuit substrates 10 and 50 are bonded. Theinsulating film is destroyed to conduct two circuits of these twocircuit substrates via the contact pads 11, 21.

In the prior art of TAB and COF, the material of the circuit substrate,which carries the integrated circuit (IC), is transparent, it assuresthe reliability of the circuit connection to observe whether the contactpads are matched and the conductive particles between the contact padsare deformed or not. But this technique cannot be applied to an opaquecircuit substrate.

In a prior art, as shown in FIG. 3 and FIG. 4, a contact pad 130 on acircuit substrate has a chink 131 at the center. In assembling the twocircuit substrates, the chink 131 is covered by the contact pad 210 asshown in FIG. 3 if the contact pads 130, 210 are matched well, whichindicates an validated circuit connection; and the chink 131 is perviousto light as shown in FIG. 4 if the contact pads 130, 210 are mismatched,which indicates a bad circuit connection. This prior art does notprovide an instant method of inspecting the reliability of the circuitconnection.

FIG. 5 is a schematic diagram showing another prior art, the dummy pads140 and a window 141 are formed on two bonded circuit substratesrespectively. The condition of matching the window 141 and the dummypads 140 indicates the reliability of circuit connection of two bondedcircuit substrates. But, this technique does not provide the instantinspection.

FIG. 6 is a schematic diagram showing the prior art, there are contactpads 210, 150 on two circuit substrates, wherein the contact pad 150 hassidewalls on its both edges to form the bonding pads 151. When thecontact pads 210, 150 are thermally compressed, the amount of theconductive particles 32, constrained between the bonding pads 151, ofthe anisotropic conductive film is enough to avoid the conductiveparticles 32 spilling to damage the conduction. Again, this prior artdoes not provide the instant inspection.

The quality of contact-pad connection affects the reliability of thecircuit connection of two bonded circuit substrates, and the main twofactors are whether the contact pads are matched or not and contactquality of the anisotropic conductive film. The post-fabricatedinspection is a big drawback in assembling two circuit boards. Moreespecially, in assembling the LCD, it costs and spends much to measurewhite/black dots on the screen of the LCD for inspecting the reliabilityof the circuit connection after the LCD is assembled. An instant methodof inspecting circuit connection in bonding two circuit substrates isessential for providing developers information and condition to modifythe environmental parameters to enhance the reliability of the circuitconnection.

SUMMARY OF THE INVENTION

For solving the aforementioned problems, one object of this inventionprovides a contact pad design of a bonding structure having an instantinspection ability of circuit connection in bonding two circuitsubstrates.

Another object of this invention provides an instant method ofinspecting the reliability of circuit connection in bonding two circuitsubstrates.

To achieve the above-mentioned objects, one embodiment of the presentinvention is to provide a bonding structure to bond two substrates,especially applied to assemble the circuit substrate of the liquidcrystal display and the circuit substrate carrying the drivingintegrated circuit. The bonding structure includes a first circuitsubstrate having a first circuit, wherein the end portion of the firstcircuit comprises a plurality of first contact pads transmitting signalsseparate from each other, a second circuit substrate having a secondcircuit, wherein the end portion of the second circuit comprises aplurality of second contact pads transmitting the signals separate fromeach other and each second contact pad is configured to be opposite tothe corresponding first contact pad for connecting the first circuit andis divided into a detecting part and a circuit part separated from eachother, and an anisotropic conductive film disposed between eachcorresponding first and second contact pads for connecting the firstcontact pad with the circuit part and the detecting part respectively.The anisotropic conductive film includes conductive particles and aninsulator, wherein the conductive particles are disposed of aninsulation film on their surfaces to remain insulation and distributedin the insulator.

According to one embodiment, the method of inspecting the circuitconnection of the aforementioned bonding structure of two circuitsubstrates comprises: inputting a signal into the circuit part,measuring an output signal from the detecting part and comparing thesignal inputted with the output signal, wherein the output signal andthe signal inputted are of the same type.

In two bonded circuit substrates, the signal inputted at the circuitpart passes the conductive particles to the first contact pad, and thenpasses the conductive particles again to the detecting part from thefirst contact pad. Therefore, measuring the output signal can inspectthe reliability of the circuit connection of the bonded circuitsubstrates.

If the output signal is the same as the input signal, the bondingstructure between the first contact pad and the circuit part isvalidated, or, if not, the bonding structure is invalidated.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is the top schematic drawing showing the bonding structurebetween two circuit substrates.

FIG. 2 is the explored sectional drawing showing the bonding structurebetween two circuit substrates.

FIG. 3 is the schematic drawing showing the matched state of the bondingstructure between two circuit substrates.

FIG. 4 is the schematic drawing showing the mismatched state of thebonding structure between two circuit substrates.

FIG. 5 is the schematic drawing showing the matched state of the bondingstructure between two circuit substrates.

FIG. 6 is the sectional drawing showing the bonding structure in twobonded circuit substrates.

FIG. 7 is the explored sectional drawing showing the bonding structurebetween two circuit substrates according to an embodiment of thisinvention.

FIG. 7 a is the top schematic drawing showing the bonding structurebetween two substates according to an embodiment of this invention.

FIG. 8 is the sectional drawing showing the bonding structure betweentwo bonded circuit substrates according to an embodiment of thisinvention.

FIG. 9 is the flow chart showing the inspection method according to anembodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 7 a is a top schematic drawing showing the bonding structurebetween two circuit substrates according to an embodiment, and FIG. 7 isan explored sectional diagram taken along the longitudinal direction ofthe first contact pad 110 and second contact pad 220 in FIG. 7 a. Asshown in FIG. 7 a and FIG. 7, a first circuit substrate 100 includes analignment film 420, a first circuit covered by the alignment film 420(not shown in the figure) and an insulating layer 410, where the endportion of the first circuit comprises a plurality of first contact pads110 transmitting signals separate from each other, is exposed out of theinsulating layer 410. A second circuit substrate 500 includes a secondcircuit (not shown in the figure) and an end portion thereof comprisiesa plurality of second contact pads 220 transmitting the signal separatefrom each other. Each second contact pad 220 is configured to beopposite to the corresponding first contact pad 110. By a gap 223, eachsecond contact pad 220 is divided into a circuit part 221 and adetecting part 222.

An anisotropic conductive film 300 is disposed between eachcorresponding first contact pad 110 and second contact pad 220. Theanisotropic conductive film 300 includes an insulator 310 and aplurality of conductive particles 320. Wherein, conductive particles 320are distributed in the insulator 310 and each conductive particle 320 isdisposed of an insulation film on its surface to form an insulatedparticle. Once the anisotropic conductive film 300 is thermallycompressed, the insulation surface of the conductive particle 320 isdestroyed so as to conduct the first contact pad 110 and the circuitpart 221, and to conduct the first contact pad 110 and the detectingpart 222.

The circuit part 221 is provided with a signal-inputted area 224 and thedetecting part 222 is provided with a detecting area 510. When thecircuit part 221 and the detecting part 222 are an open circuit, thesignal inputted at the signal-inputted area 224 may not be transferredor measured at the detecting area 510. In order to confirm that thesignal from the circuit part 221 does pass through the first contact pad110 to the detecting part 222, the gap 223 should be wider than thediameter of the conduct particle 320 in the anisotropic conductive film300.

Referring to FIG. 7 and FIG. 8 for illustrating the conduction principleof the circuit. When the first circuit substrate 100 and the secondcircuit substrate 500 are thermally compressed, the insulation surfacesof the conductive particles 320 are destroyed to conduct the firstcontact pad 110 and the circuit part 221, and to conduct the firstcontact pad 110 and detecting part 222. However, the conductiveparticles 320 distributed in the gap 223 are not destroyed to remaininsulation because of the diameter smaller than the gap 223. Thus, thecircuit part 221 is electrically connected to the first contact pad 110via the conductive particles 320, and the detecting part 222 iselectrically connected to the first contact pad 110 via the conductiveparticles 320. Therefore, the circuit connection of these two circuitsubstrates 100, 500 can be validated by measuring the signal inputted atthe circuit part 221 at the detecting part 222.

By accompanying FIG. 8 and FIG. 9, the following explains the instantinspection method:

Step 710 is to input a signal at the circuit part 221 of the secondcircuit substrate 500.

Step 720 is to measure an output signal at the detecting part 222. Thesignal is inputted at the circuit part 221 of the second circuit (notshown in the figure) on the second circuit substrate 500, and passesthrough the conductive particles 320 of the anisotropic conductive film300 to the first contact pad 110 on the first circuit substrate 100.Then, the signal passes through again the conductive particles 320 ofthe anisotropic conductive film 300 from the first contact pad 110 tothe detecting part 222 on the second circuit substrate 500.

Step 730 is to compare the signal inputted at the circuit part 221 withthe output signal at the detecting part 222. If the output signal is thesame as the input signal, the bonding structure between the firstcontact pad 110 and the circuit part 221 is validated, otherwise thebonding structure is failed.

This invention may be employed generally to the bonding structure of thebonded circuit substrates. Wherein, each of the circuit substrates isthe insulation circuit substrate, such as the printed circuit board,plastic circuit substrate, glass circuit substrate or flexible circuitsubstrate, like the tape carrier package substrate, and so on. No matterwhat the bonded circuit substrates are transparent or not, the bondingstructure can be employed to have the instant circuit connectioninspection in bonding these circuit substrates to provide a higherreliability than that in the conventional eye-observation method.

For a liquid crystal display, even a flexible panel, the circuitsubstrate carrying the driving integrated circuit may be implemented asthe first circuit substrate. The circuit substrate carrying the arraycircuit of the LCD may be implemented as the second circuit substrate.Once this invention is applied in bonding the two circuit substrates,the bonding structure of the display has the instant inspecting abilityof circuit connection for the bonding structure.

Although the present invention has been explained in relation to itspreferred embodiment, it is to be understood that other modificationsand variation can be made without departing the spirit and scope of theinvention as claimed.

1. An instant circuit inspection method, applied to inspect thereliability of a circuit connection of a bonding structure of twocircuit substrates, comprising the steps of: providing the bondingstructure comprising: a first circuit substrate having a first circuit,wherein an end portion of the first circuit comprises a plurality offirst contact pads transmitting signals separate from each other; asecond circuit substrate having a second circuit, wherein an end portionof the second circuit comprises a plurality of second contact padstransmitting the signals separate from each other and each secondcontact pad is configured to be opposite to the corresponding firstcontact pad for connecting the first circuit, and is divided into acircuit part and a detecting part by a gap; and an anisotropicconductive film disposed between each corresponding first and secondcontact pad, wherein the gap is wider than the diameter of the conductparticle in the anisotropic conductive film; the detecting part iselectrically connected to the circuit part by the anisotropic conductivefilm and the first contact pad; and the single first contact pad issimultaneously electrically connected to the circuit part and thedetecting part; performing inspection procedures to each of the secondcontact pads, wherein the inspection procedures comprises: inputting asignal to the circuit part of the second contact pad; measuring anoutput signal from the detecting part of the second contact pad; andcomparing the output signal with the signal inputted, wherein the outputsignal and the signal inputted are of the same type.
 2. An instantcircuit inspection method according to claim 1, wherein during the stepof comparing the output signal with the signal inputted, the bondingstructure of two bonded circuit substrates is validated to beelectrically connected if the output signal is the same as the signalinputted, otherwise, the bonding structure is invalidated to beelectrically connected.
 3. An instant circuit inspection method, appliedto inspect the reliability of a circuit connection of a bondingstructure of two circuit substrates, comprising the steps of: providingthe bonding structure comprising: a first circuit substrate having afirst circuit, wherein an end portion of the first circuit comprises aplurality of first contact pads transmitting signals separate from eachother; a second circuit substrate having a second circuit, wherein anend portion of the second circuit comprises a plurality of secondcontact pads transmitting the signals separate from each other and eachsecond contact pad is configured to be opposite to the correspondingfirst contact pad for connecting the first circuit, and is divided intoa circuit part and a detecting part by a gap; and an anisotropicconductive film disposed between each corresponding first and secondcontact pad, wherein the gap is wider than the diameter of the conductparticle in the anisotropic conductive film; the detecting part iselectrically connected to the circuit part by the anisotropic conductivefilm and the first contact pad; and the single first contact pad issimultaneously electrically connected to the circuit part and thedetecting part; performing inspection procedures to each of the secondcontact pads, wherein the inspection procedures comprises: connectingone end of a signal source to the circuit part of the second contactpads; connecting one end of a meter to the detecting part of the secondcontact pad; connecting the other end of the meter to the other end ofthe signal source; inputting a signal to the circuit part; measuring anoutput signal from the detecting part; and comparing the output signalwith the signal inputted, wherein the output signal and the signalinputted are of the same type.